1. Field of the Invention
The present invention relates to a liquid discharge recording head including highly accurate flow paths that have a low stress and satisfactory chemical resistance and that are formed by patterning with ultraviolet irradiation or the like, and a liquid discharge apparatus including the same.
2. Description of the Related Art
An example of liquid discharge apparatuses is an ink-jet printer apparatus that discharges, for example, ink as a liquid and that employs an ink-jet recording method (liquid-jet recording method). Such an ink-jet printer apparatus includes an ink-jet recording head for discharging ink. The ink-jet recording head includes a plurality of constituent units each composed of a discharge port (i.e., orifice) that discharges ink in the form of a minute droplet, a flow path communicating with the orifice, and an ink-discharge-pressure-generating element provided on a part of the flow path. In order to produce high-quality images using such an ink-jet recording head, small droplets of ink discharged from the orifices are preferably discharged from each orifice at a constant volume and a constant discharging rate.
Examples of ink-jet recording heads that meet the above discharging conditions include ink-jet recording heads described in Japanese Unexamined Patent Application Publication Nos. 56-123869, 57-208255, and 57-208256. In the ink-jet recording heads described in Japanese Unexamined Patent Application Publication Nos. 56-123869, 57-208255, and 57-208256, ink flow paths and nozzles composed of orifice parts are formed on a substrate having ink-discharge-pressure-generating elements by patterning a photosensitive resin material or a photoresist, and a cover such as a glass plate is bonded on the component having the ink flow paths and the nozzles. Examples of the photosensitive resin material and the photoresist include photopolymers using photopolymerization of a diazo resin, p-diazoquinone, or a vinyl monomer in the presence of a polymerization initiator; dimerization-type photopolymers using a reaction of polyvinyl cinnamate or the like and a sensitizer; mixtures of orthoquinone diazide and a phenol novolak resin; mixtures of polyvinyl alcohol and a diazo resin; polyether photopolymers prepared by copolymerizing 4-glycidylethylene oxide with benzophenone or glycidylchalcone; copolymers of N,N-dimethylmethacrylamide and, for example, acrylamide benzophenone; unsaturated polyester photosensitive resins; unsaturated urethane photosensitive resins; photosensitive compositions prepared by mixing a bifunctional acrylic monomer, a photoinitiator, and a polymer; dichromate photoresists; non-chromium water-soluble photoresists; and polyvinyl cinnamate photoresists.
Another example of an ink-jet recording head that meets the above discharging conditions is an ink-jet recording head produced by a method described in Japanese Unexamined Patent Application Publication No. 61-154947. According to the method of producing an ink-jet recording head described in Japanese Unexamined Patent Application Publication No. 61-154947, a pattern of ink flow paths is formed on a part of a substrate, the part in which the ink flow paths are formed, using a soluble resin; the pattern of the ink flow paths is covered with an epoxy resin or the like; the substrate is cut; and the soluble resin forming the pattern of ink flow paths is then removed by dissolving, thereby producing the ink-jet recording head.
In the ink-jet recording heads described in Japanese Unexamined Patent Application Publication Nos. 56-123869, 57-208255, 57-208256, and 61-154947, for example, a heating resistor, which serves as an ink-discharge-pressure-generating element provided on a part of an ink flow path, is provided in a direction parallel to the flow of ink. Each orifice that discharges the ink is provided at an end of the corresponding ink flow path and in a direction perpendicular to the flow of the ink. In such ink-jet recording heads, the orifice is disposed so as to be substantially perpendicular to the heating resistor. Consequently, the discharge direction of ink is perpendicular to the growth direction of a bubble formed on the heating resistor. That is, the growth direction of the bubble is different from the discharge direction of the ink.
In such ink-jet recording heads, since a part of an orifice disposed at an end of the corresponding ink flow path is formed of an end of a substrate, the distance between the ink-discharge-pressure-generating element and the orifice is determined by cutting of the substrate. Therefore, in controlling the distance between the ink-discharge-pressure-generating element and the orifice, the accuracy with which the substrate is cut is very important. The substrate is generally cut with a mechanical device such as a dicing saw, and it is difficult to realize high accuracy with such a mechanical device.
Unlike the ink-jet recording heads described in Japanese Unexamined Patent Application Publication Nos. 56-123869, 57-208255, 57-208256, and 61-154947, in other ink-jet recording heads, for example, an electrothermal conversion element, which is an ink-discharge-pressure-generating element, is provided so as to face an orifice. Thus, the growth direction of a bubble formed on the electrothermal conversion element is substantially the same as the discharge direction of ink. For example, Japanese Unexamined Patent Application Publication Nos. 58-8658 and 62-264957 describe such ink-jet recording heads. In the ink-jet recording head described in Japanese Unexamined Patent Application Publication No. 58-8658, a dry film serving as an orifice plate is bonded to a substrate having electrothermal conversion elements, with another patterned dry film therebetween, and orifices are formed on the dry film serving as the orifice plate by photolithography at positions facing the electrothermal conversion elements. In the ink-jet recording head described in Japanese Unexamined Patent Application Publication No. 62-264957, a substrate having ink-discharge-pressure-generating elements is bonded to an orifice plate produced by electroforming, with a patterned dry film therebetween.
In the ink-jet recording heads described in Japanese Unexamined Patent Application Publication Nos. 58-8658 and 62-264957, the orifice plate has a small thickness of, for example, 20 μm or less, and it is difficult to produce the orifice plate uniformly. Furthermore, in these ink-jet recording heads, even when the orifice plate can be produced, it is extremely difficult to perform the process of bonding with the substrate having ink-discharge-pressure-generating elements because of the brittleness of the orifice plate.
Furthermore, regarding discharging conditions in ink-jet recording heads, it is necessary not only to discharge ink from orifices at a constant volume and a constant discharging rate, but also to discharge minute ink droplets at precise positions. In ink-jet recording heads, in order to discharge ink at precise positions, the distance between an electrothermal conversion element provided at a discharge-energy-generating part and an orifice (hereinafter referred to as “OH distance”) is preferably small.
An example of a method of producing an ink-jet recording head having a highly precise OH distance is a method described in Japanese Unexamined Patent Application Publication No. 6-286149. This patent document describes a method of producing an ink-jet recording head including the steps of forming an ink flow path pattern that forms ink flow paths on a substrate having ink-discharge-pressure-generating elements using a soluble resin, forming a covering resin layer that forms an ink flow path wall on the soluble resin layer by performing solvent coating of a solution, prepared by dissolving a covering resin containing an epoxy resin that is a solid at room temperature in a solvent, on the soluble resin layer constituting the ink flow path pattern, forming orifices on the covering resin layer disposed on an upper part of each of the ink-discharge-pressure-generating elements, and removing the soluble resin layer constituting the ink flow path pattern by dissolving. In the method of producing an ink-jet recording head described in this patent document, in view of the formation of a pattern having a high aspect ratio and a property of ink resistance, a cationic polymer of an alicyclic epoxy resin is used as the covering resin.
In ink-jet recording heads, the use of the methods and the materials described in Japanese Unexamined Patent Application Publication Nos. 6-286149 and 7-214783 causes the following additional problems.
The cured product prepared by cationic polymerization of such an alicyclic epoxy resin has excellent adhesive force with a base substrate. However, because of a high internal stress of the cured product, the covering resin layer made of the cured product is peeled off from the base substrate. Furthermore, in the cured product prepared by cationic polymerization of an alicyclic epoxy resin, cracks (film breakages) are also generated particularly in the vicinity of a corner, e.g., a pattern edge, of the resin film on which a stress is concentrated, thereby significantly degrading the reliability as an ink-jet recording head. In addition, some of these materials have insufficient patterning performance and do not provide the minute patterning performance for forming the structure of an ink-jet recording head.
In ink-jet recording heads, in particular, when the covering resin layer serving as an ink flow path wall is formed so as to have an elongated shape or a large thickness, and when the ink flow path has a minute and complex structure, the covering resin layer is easily peeled off or cracks on the covering resin layer are easily generated. Furthermore, in ink-jet recording heads, in order to maintain the image quality, the head surface from which ink is discharged is cleaned so as to remove extra ink adhered to the head surface. In the head cleaning of an ink-jet recording head, since the head surface is wiped with a cleaning component or the like, a mechanical load is applied to the head surface, which may accelerate the removal of the covering resin layer from a substrate.